MIC29311 Datasheet, PDF (9/12 Pages) Micrel Semiconductor – 3A Fast-Response LDO Regulator for USB Preliminary Information

MIC29311
“Typical Application”). USB requires that the downstream
voltage supplied to peripherals from a self-powered hub is
between 4.75V and 5.25V. The MIC29311 provides regula-
tion with this requirement. The enable pin input controls
ganged power for up to seven downstream ports, each
drawing up to 500mA. The device has an output current
limiting circuit that linearly decreases the output voltage as
the output current exceeds 3A. When the part is out of
regulation by 5%, the error flag goes low and signals a fault
condition to the microcontroller, allowing the system to be
disabled. This provides the overcurrent protection that is
required by USB.
In Figure 2, the MIC29311 provides power to the MIC2527
quad power switches. The MIC2527 provides power switch-
ing to four independently controlled downstream ports. Two
MIC2527s can be used to provide a 6-port, self-powered hub
in conjunction with the MIC29311. The 5.1V output of the
MIC29311 is optimized to ensure that under maximum load
condition, the output voltage of each channel of the MIC2527
remains above 4.75V. This is the minimum voltage require-
Micrel
ment for self-powered USB hubs. The output voltage is a
function of the minimum output voltage of the power supply,
the PCB trace resistance and the on-resistance of the switch.
Table 1 shows the maximum allowable on-resistance for a
5.1V power supply in a self-powered hub, assuming 30mV of
voltage drop due to PCB trace resistance. The 5.1V of the
MIC29311 and the 300mΩ on-resistance of each MIC2527
switch provides an economical solution to power manage-
ment of self-powered hubs.
Nominal Supply
Voltage Tolerance
1%
2%
5.10V
3%
4%
5%
Minimum
Voltage
5.05V
5V
4.95V
4.9V
4.85V
Maximum Maximum
Voltage
R_ON
5.15V 540mΩ
5.2V
440mΩ
5.25V 340mΩ
5.3V
—
5.36V
—
Table 1. Max. Allowable On-Resistance
For further information concerning USB power management,
refer to Application Note 17 and Application Hint 30.
5.7V
MIC29311-5.1
LDO Regulator
IN
OUT
5.1V ±3%
EN ERR
GND
10k
MIC5207-3.3
LDO Regulator
IN
OUT
4.7
µF
1µF
GND
3.3V USB Controller
V+
ON/OFF
OVERCURRENT
D+
D– _GND
Bold lines indicate
0.1" wide, 1-oz. copper
high-current traces.
* 33µF, 16V tantalum or 100µF, 10V electrolytic per port
47k
MIC2527
ENA
IN
FLGA
IN
ENB OUTA
FLGB OUTB
ENC OUTC
FLGC OUTD
END
FLGD
GND
GND
33µF*
0.1
µF
33µF*
33µF*
33µF*
Ferrite
Bead
0.01µF
4.75V min.
at 500mA
V_BUS
D+
D–
GND
0.01µF
V_BUS
D+
D–
GND
0.01µF
V_BUS
D+
D–
GND
0.01µF
V_BUS
D+
D–
GND
Downstream
USB
Port 1
500mA max.
Downstream
USB
Port 2
500mA max.
Downstream
USB
Port 3
500mA max.
Downstream
USB
Port 4
500mA max.
Figure 2. 4-Port Self-Powered Hub
December 1998
9
MIC29311